A Boston-bound man arrested at Los Angeles International Airport wearing what appeared to be a bulletproof vest and transporting weapons in his luggage puzzled investigators by saying, "Hey, this is a game."

Yongda Huang Harris, 28, a naturalized U.S. citizen who teaches English in China, was otherwise uncooperative with detectives and the FBI, which had an agent sit in on the questioning at the airport.

One of them told ABC News, "It could mean he thought the questioning was a game. He could mean the whole thing -- the vest, the stuff in his checked baggage, was a game."

At least once during his flights from China to Korea to Japan and on to Los Angeles, Harris set off alarms and underwent secondary screening, authorities told ABC News.

Harris was found to be carrying body armor when he was screened in Korea, law enforcement officials told ABC News. He was allowed to board his flight to LAX after he and his carry-on luggage were thoroughly searched and nothing prohibited or dangerous was found.

Following that screening, it appeared that Harris continued wearing his vest all the way to the United States, where he was stopped and detained upon entry.

Harris told U.S. investigators that he was puzzled that they would hassle him over his wearing of the vest and asked them why they were doing so after he had been stopped in Korea and in Japan and allowed to proceed.

The bulletproof-style vest, in fact, "would not have stopped a bullet," according to U.S. authorities. It was a Chinese-made knockoff of a vest and not, in fact, an actual ballistic vest, investigators said.

"There is no reason to believe he did not have it on when he began the trip in China," one senior investigator said. "We believe he boarded with it. The question is how did it happen."

Harris was pulled aside in customs Friday at the Los Angeles airport for a secondary baggage inspection, when an officer noticed Harris was wearing the vest.

The officer asked Harris if he had anything he would like to declare in his checked luggage. Harris told the officer he had a knife.

When his bag was searched, the officer found an array of suspicious items -- including a smoke grenade, three leather-coated black-jack billy clubs, a collapsible baton, a full-face respirator, several knives and a hatchet. Officers also found body bags, a tyvex biohazard suit, various masks, duct tape, handcuffs, leg irons, flex cuffs, oven mitts and cooking tongs.

It was not clear why Harris had the items.

On Harris' laptop, investigators found Japanese fantasy rape writings, pornography and a copy of the "Poor Man's James Bond," a popular text among dissidents and anarchists that has exhaustive information on the use of terror tactics.

Harris earlier in 2012 was in Japan on a trip that lasted approximately 10 or 11 days.

Investigators also found on Harris' hard drive a copy of a GMATs study guide, investigators said. And they found a site guide to Islamic burial sites in Japan. Here, too, detectives could not determine what if any meaning beyond a curiosity the guide might hold.

The smoke grenade, manufactured by a company called Commando, is classified as an explosive and is capable of filling a 40,000-cubic-foot space with smoke, according to a federal affidavit. The grenade is also capable of causing a fire.

A homeland security official told ABC News it is not likely that a smoke grenade could bring down an aircraft and stressed that while a smoke grenade is a prohibited item, it was in the checked luggage and not accessible to Harris.

There is no indication, the official said, that Harris intended to harm the aircraft.

Nevertheless, the TSA is working with Korean authorities to determine how a prohibited item -- the smoke grenade -- was allowed on to the plane.

According to authorities, Harris began his latest trip in China, where he purchased a one-way ticket to Korea.

In Korea, he purchased the ticket that took him through Japan to LAX. His final destination was to be Boston, authorities said.

The China ticket information did not appear in a federal affidavit on the case because that leg of the trip wasn't immediately apparent from the U.S.-bound ticket authorities first found in Harris' possession.

Harris, when detained, was questioned by a series of detectives before invoking his right to counsel. Officials described him as savvy and closed.

Harris only made his one potentially relevant statement -- "almost like he was talking to himself" -- when he relaxed during an interview with one detective who had a family member that had the same last name as his mother's maiden name, sources said.

Though he was arrested Friday, because of the federal holiday Harris made his initial appearance Tuesday in a Los Angeles federal court and remained in federal custody. Harris was scheduled to be back in court Friday for a detention hearing.

The FBI, according to officials, has notified its legal attaches in both China and Japan of the troubling materials they found with Harris, the pornographic pictures and writings on his computer and the concerns given his close proximity to children in his teaching role.

The FBI asked its counterparts to look into a number of areas and advised them of Harris' interest in pornography and fantasy rape in the hope that it might provide additional avenues for investigation.

The Department of Homeland Security and the Transportation Security Administration also are looking into the matter and how it could have been avoided.

"TSA will review, in concert with aviation security officials in Korea, how a prohibited item was able to travel in checked baggage and implement any necessary changes," DHS Director of Communications Matt Chandler said.

Harris came to the United States as a child, was raised in the Boston area and attended Boston University. He had an interest in science, investigators said, and calculations or formulas were found in a diary in his possession.

Harris was being represented by criminal defense attorney Steven A. Seiden, who is also representing the controversial anti-Islam filmmaker Nakoula Basseley Nakoula.

Reached for comment, Seiden's office described Harris as a highly intelligent and diligent student who attended excellent schools in Boston and has no criminal history or violent tendencies.

"I will speak about Mr. Harris on Friday when I know more about Mr. Harris and what I might say at that time," Seiden said Wednesday. "Thank you."